Sheet advance apparatus

ABSTRACT

Apparatus for intermittently advancing successive equivalent length portions of a generally continuous thermoplastic sheet through upstream article forming and trimming stations. An indexing mechanism in the drive train controls the forward velocity of a carriage on which the sheet is clamped. Fixed stops precisely define the extent of forward movement of the carriage. A resiliently biased plunger in the means for interconnecting the drive train to the carriage absorbs the incremental and variable additional movement of the drive train caused by tolerances therein, after forward movement of the carriage and therefore of the sheet have been positively terminated through contact with the fixed stops.

United States Patent [72] Inventors Frank M. Kulig Bloomfield; Lee R.Layman, Windsor Locks, both of Conn. [21] Appl. No. 849,780 [22] FiledAug. 13, 1969 [45] Patented Oct. 19, 1971 [73] Assignee Monsanto CompanySt. Louis, Mo.

[54] SHEET ADVANCE APPARATUS 12 Claims, 5 Drawing Figs.

[52] US. Cl 226/162, 18/ 1 9 P [51] Int. Cl B65h 17/36 [50] FieldofSearch 226/158, 143, 162-466 [5 6] References Cited UNITED STATESPATENTS 2,978,160 4/1961 Bunnell 226/162 X 3,412,995 4/1968 ParupsABSTRACT: Apparatus for intermittently advancing successive equivalentlength portions of a generally continuous thermoplastic sheet throughupstream article forming and trimming stations. An indexing mechanism inthe drive train controls the forward velocity of a carriage on which thesheet is clamped. Fixed stops precisely define the extent of forwardmovement of the carriage. A resiliently biased plunger in the means forinterconnecting the drive train to the carriage absorbs the incrementaland variable additional movement of the drive train caused by tolerancestherein, after forward movement of the carriage and therefore of thesheet have been positively terminated through contact with the fixedstops.

PAIENIEDUBI 19 I911 SHEET 1 [IF 2 INVUN H )RS FRANK M. KULIG LEE R.LAYMAN ATTORNEY PATENTEUUBT 19 I97| SHE em: 2 v 3,513,980

m 0mm T K Y N .A W

K R W M E E m L HHWJ W ATTORNEY SHEET ADVANCE APPARATUS BACKGROUND OFTHE INVENTION This invention relates in general to improvements inequipment for forming articles from plastic sheet, and in particular toimprovements in apparatus for advancing the sheet through the articleforming and trimming presses.

Several different types of forming operations using heat and pressureare presently carried out on generally continuous plastic sheet tosimultaneously form large numbers of articles, for example containers,in a single cycle. One type of operation is by pneumatic pressuredifferential forcing of segments of a large section of the sheet intofemale, or over male molds in a forming press, either with or withoutmechanical assistance, to shape the articles while leaving themperipherally attached to the sheet in order to permit convenient,simultaneous conveying of all of the articles out of the forming pressas the sheet section is advanced to a further downstream position. Thesheet with the articles still attached therein is then positioned withina trimming press intermediate a series of oppositely aligned punch anddie members. The punches are then caused to advance toward the dies orvice versa whereupon a sharp edge on one or the other simultaneouslysevers each of the articles from the sheet leaving them free to beconveyed to a suitable collection station. The remainder of the sheetsection, which now consists of a web made up of the portions of thesheet section intermediate the articles, is then advanced once again,generally to a scrap recovery unit. This type of sheet shaping is knownas post trim forming, since the articles are from the sheet downstreamof the forming equipment. The apparatus utilized to advance the ratherflexible sheet through the forming and trimming presses is generallylocated downstream of the trim press and operates by pulling on the websection which has had the articles removed therefrom, so as tointermittently advance upstream portions of the sheet through theforming and trimming presses.

Needless to say, it is extremely important that each of the large numberof formed articles formed and attached in the sheet during a cycle ofthe equipment be centered as accurately as possible between the opposedsevering members of the trim press. Otherwise, when the movable portionof the press is advanced towards the stationary portion in carrying outthe trimming operation, any misaligned articles will be either partiallyor completely crushed between the cooperating members, or else unevenlytrimmed depending on the extent of variation from the desiredregistration position. Also, it is desirable that the sheet be rapidlyadvanced through the various stations of the equipment to minimize cycletime, yet as smoothly as possible, since portions of the sheet beingpulled are at elevated temperature and can deform under the tensionbeing exerted by the sheet advance equipment. This deformation canproduce thickness irregularities in the formed articles and isespecially critical when the sheet is preheated prior to entry into theforming press.

Now there has been developed a unique apparatus which provides rapid yetsmooth sheet advancement and accurate sheet registration in upstreamequipment.

Accordingly, it is a principal object of this invention to provide animproved sheet advance apparatus component for use in an equipmentsystem for forming articles from plastic sheet.

An additional object of this invention is to provide an improvedapparatus for intermittently advancing successive equivalent lengthportions of a generally continuous thermoplastic sheet through upstreamarticle forming and trimming stations which is capable of extremely finerepeatability.

A further object of this invention is to provide apparatus of theaforementioned variety wherein the precision of the extent of sheettravel is generally independent of the tolerances of the means forintermittently moving the sheet.

An additional object of this invention is to provide apparatus of theaforementioned variety wherein the precision of the extent of sheetmovement is positively determined by abutments defining the limits ofsheet travel.

A further object of this invention is to provide apparatus of theaforementioned variety wherein sheet movement is rapid yet smooth in thesense that it is free of abrupt starts and stops.

Other objects of this invention will in part be obvious and will in partappear hereinafter.

SUMMARY OF THE INVENTION These and other objects are accomplished byproviding apparatus for intermittently advancing successive equivalentlength portions of a thermoplastic sheet which comprises a frame, a pairof horizontally disposed elongated support members on the frame, acarriage mounted for reciprocative movement on the support members,means on the carriage for gripping the sheet, drive means forintermittently moving the carriage forward including an indexingmechanism for controlling the velocity of the carriage during itsforward movement so as to advance the sheet smoothly when engaged by thegripping means, means interconnecting the carriage to the drive means,means for reversing the forward movement of the carriage, and stops fordelimiting the reciprocative movement of the carriage.

The means interconnecting the carriage to the drive means preferablycomprise three pusher assemblies, each fastened to an endless drivechain at spaced, equidistant intervals about the periphery of the chainand a reciprocatably mounted drive rod on the carriage adapted toconsecutively engage each of the three pusher assemblies at the start ofthe forward movement of the carriage for successive cycles. Each pusherassembly includes a block fastener to the chain and a plunger mounted inthe block adapted to engage the drive rod on the carriage to move thecarriage forward, the plunger being resiliently biased in the directionof forward movement of the carriage.

Means are provided to decelerate the forward movement of the carriageprior to its engagement with one of the stops, these means including apivotally mounted latch on the carriage adapted to engage the rear sideof the block of the particular pusher assembly then moving the carriage.

BRIEF DESCRIPTION OF THE DRAWINGS In describing the overall invention,reference will be made to the accompanying drawings in which:

FIG. I is a front view of the apparatus of the present invention;

FIG. 2 is a side view of the apparatus of FIG. 1;

FIG. 3 is a plan view of the apparatus of FIG. I with the sheet removed;

FIG. 4 is an exploded perspective view of a portion of the apparatus ofFIG. I; and

FIG. 5 is a partial, schematic view with parts broken away of theapparatus portion of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings, wherein identical numerals refer to identical parts, there isshown in FIGS. 1-3, apparatus generally indicated as 10 forintermittently advancing successive equivalent length portions of asheet S of thermoplastic material through known, conventional upstreamforming the trimming stations (not shown). Apparatus 10 comprises aframe, generally indicated as 12, for supporting the working componentsthereof. Frame 12 comprises bedplate 14 to which are fastened fourstanchions 16, each extending upwardly from the surface of bedplate 14in the corners thereof. Stringers 18 connect the upper ends of each pairof stanchions 16 at opposite ends of the frame. Gussets 17 may be usedto strengthen the joints between the stanchions l6 and the bedplate l4.

Apparatus 10 further comprises a pair 20 of horizontally disposed,elongated support members cylindrical in cross section and connected ateither end to stringers 18 of frame 12. Carriage 22 is mounted forreciprocative movement on members 20 from a rear position situated atthe left end of FIG. 1 to a forward position situated at the right endof FIG. 1. Carriage 22 comprises horizontal platform 24 having dualconnecting members 26 depending from the under side thereof. Members 26have cylindrical openings extending therethrough such that platform 24may be mounted by means of members 26 and ball bushings 27 for extremelylow friction transverse movement along support members 20. Carriage 22further comprises a pair of oppositely aligned yokes 28 fastened to theunder side of platform 24 at the outer margins thereof.

Means 30 are provided on carriage 22 for gripping a limited portion ofsheet S along its outer margins. Means 30 comprises oppositely alignedsupport blocks 32 mounted on the outer margin of the upper surface ofplatform 24, which in turn carry fingers 34 reciprocatably mounted onpiston rods 35, which are conventionally operative by suitable fluidpressure introduced to piston housings 36. Fingers 34 may have upturnedend portions as depicted in FIG. 1, which serve as a lead in to avoidripping sheet S as it is being engaged by the fingers.

Drive means, generally indicated as 38, are provided for intermittentlymoving carriage 22 from a rear position at the left of FIG. 1 to anadvance position at the right of FIG. 1. Drive means 38 includes aconventional DC motor 40, having its output shaft coupled to aconventional clutch-brake mechanism 41. The output of mechanism 41 isconnected through a stepdown gear reducer 44 to an indexing assembly 42which controls the velocity of carriage 22 during its forward movementin such a manner as to advance the sheet smoothly when engaged bygripping means 30. Clutch-brake mechanism 41 is of a conventionalvariety and serves to supply intermittent rotary motion from motor 40 togear box 44 on demand. Though an AC motor can be used, a DC motor ispreferred for flexibility since its shaft speed may be changed primarilyby varying the voltage input. Indexing mechanism 42 likewise is of aconventional variety. Commercially available models are obtainable, forexample, the Trans-pac II model produced by Ferguson Machine Co. of St.Louis, Missouri. Indexing mechanism 42 has replaceable internal camcomponents which serve to vary the rotary speed of its output shaft 46from that of its input shaft. When this varying rotary speed iseventually transmitted to carriage 22, the velocity of the latter andtherefore of the sheet held in place thereon will gradually increase.After an adjustable interval along its forward path, mechanism 42,through suitable interconnecting means to be hereafter described, thenserves to decelerate the forward movement of carriage 22 and thereforeof the gripped sheet, so as to avoid the consequences (for examplebuckling) of any sudden stop on completion of the intermittent sheetadvance cycle. Output shaft 46 of indexing mechanism 42 of drive means38 has an indexer drive gear 48 thereon which intermeshes with drive car50 which in turn is conventionally connected to drive shaft 52. Drivegear 50 is sized to rotate 360 for each indexing movement of mechanism42. Drive shaft 52 is conventionally mounted in pillow blocks 53 onsupports 54, which in turn are fastened to plate 56. Drive means 38further comprises drive sprockets 58 on either end of drive shaft 52,idler sprockets 60 on either end of idler shaft 62 and drive chains 64interconnecting drive and idler sprockets 58 and 60. Thus it is seenthat as DC motor 40 is activated, the rotary motion of its output shaftis transmitted through intermediate means to rotate drive sprockets 58,which in turn rotate chains 64 and therefore idler sprockets 60, andidler shaft 62.

Apparatus 10 further comprises means (FIGS. 4 and 5) for interconnectingcarriage 22 to drive means 38. These interconnecting means comprisethree pusher assemblies 68 (FIGS. 1, 4 and 5) on each side of theapparatus, fastened to endless drive chains 64 at spaced, equidistantintervals about the periphery of chains 64. These interconnecting meansfurther comprise dual, reciprocatably mounted drive rods 70 on theunderside of platform 24 of carriage 22, adapted to consecutively engageone pair of the pusher assemblies at the start of the forward movementof carriage 22. Drive rods 70 are positioned such that end portions 72(FIG. 5) move in ears 73 and through the U-shaped cavity of yokes 28(FIG. 2) in response to a suitable conventional control signal appliedto fluid operated pistons in housings 74. Each pusher assembly comprisesa block 76 (FIGS. 2 and 5) fastened to chain 64 by conventional means.Each block 76 has a plunger 78 mounted therein adapted to engage driverod 70 to move carriage 22 forward. Plunger 78 has a shank portion 80and an enlarged end portion 82 having a cutout formed therein, thesurface of which engages drive rod 70. Helical compression spring 83resiliently biases plunger 78 in the direction of forward movement ofcarriage 22, as generally indicated in FIG. 5, which represents theposition of plunger 78 at the completion of the forward movement of thecarriage. Each pusher assembly also has dual cam followers 84 mountedoutboard of block 76. Elongated cams 86 (FIG. 1) are supported onstanchions 16 on either side of the apparatus and have tracks 88 formedtherein adapted to accept followers 84 for travel therein to guide andsupport chains 64 as they turn.

Means are also provided for reversing the forward movement of carriage22 to return it to its rearmost position at the left of FIG. 1. Thesemeans comprise a flexible member 90 connected at one end to platform 24of carriage 22 and at its other end to dead weight 92. One or morerotatably mounted pulleys 94 are supported, for example on stringer 18,by means of clip 96 and are adapted to peripherally engage member 90intermediate its ends, so as to urge carrier 22 under the influence ofdead weight 92 in the opposite direction from its forward movement afterdisengagement of the advanced portion of sheet S.

Stops are provided for delimiting the reciprocative movement of carriage22. These stops comprise adjustably mounted rear stop 98 at the left endof apparatus 10 and a pair of fixed forward stops 100, convenientlyfastened to a suitable support at the forward end of the apparatus, forexample to a surface of cam 86. The distance between the carriagecontacting portions of stops 98 and 100 is exactly equivalent to theextent to which it is desired to move the sheet forward during one cycleof the apparatus. Rear stop 98 is threadably connected by means of rod102 in coupling 104, which in turn is mounted on stringer 18, such thatit is manually adjustable in the direction of the path of movement ofthe carriage, in order to permit varying the starting position ofcarriage 22 on support members 20, and thereby the overall extent ofmovement of the sheet. Adjustable stop 98 is vertically positioned so asto obstruct further movement of platform 24 as it is pulled to the rearunder the influence of weight 92.

Means are also provided to transmit to carriage 22, the decreasedangular velocity of the output shaft of indexing mechanism 42 as itapproaches completion of one cycle, thereby decelerating carriage 22during the latter portion of its forward movement. These means include apair of latches (FIG. 4) 106, each being pivotally mounted on the outersurface of a yoke 28, and having a stepped end portion 107 adapted toengage the rear side 108 of each block 76 of a pusher assembly duringthe forward movement of carriage 22. Also provided are means forpositioning each latch 106 to the left (FIG. 1) of the rear side 108 ofeach block 76 of a pusher assembly prior to the start of forwardmovement of carriage 22, such that it will be in position to laterengage side 108 at some point in the forward movement. These meansinclude a cam follower 110 on each latch 106 and a fixed elongated cam112 for each follower 110 suitably mounted, for example on cam 86,adjacent the rear end of the apparatus. Cam 112 has an upwardly inclinedtrack 114 formedtherein (FIG. 1) so as to elevate pivotally mountedlatch 106 above the particular block 76 of a pusher assembly which is tonext engage drive rod 70 for the next forward movement of the carriage.Thus as carriage 22 moves toward the forward end of the apparatus, latch106 will ride along track 114 of earn 112 such that when block 76 isbeyond end 116 (FIG. 1) of cam 112, latch 106 has left track 114, and ispositioned suchthat stepped end portion 107 may strike against side 108of block 76, in view of the fact that the forward velocity of block 76is reducing under the influence of indexing mechanism 42. Latch 106thereby transmits this reduced velocity to carriage 22 on which it ismounted. A suitable enlargement, e.g. a small boss, may be provided onthe outer surface of each yoke 28 on which a latch 106 is mounted toprevent the latch from pivoting too far downwardly after the drivepiston 70 and plunger 78 are disengaged at the completion of the forwardmovement of the carriage, and which would otherwise cause latch 106 toavoid track 114 of cam 112 on the rearward stroke of the carriage.

When it is desired to change the extent of advancement of the sheet fora cycle, in addition to varying the position of adjustable stop 98,drive and idler sprockets 58 and 60 are changed in size and links eitherremoved from or added to chains 64 as necessary to adjust the pitchdistance between sprockets. In doing so, tension on each chain 64 isrelieved by backing off jackscrews 118 (FIG. 1) toward drive sprockets58, thereby allowing idler sprocket pillow blocks 120 to be movedlaterally toward drive sprockets 58 by loosening suitable bolts holdingpillow blocks 120 on support 122, the bolts being situated in laterallyextending slots (not shown). After replacement of the sprockets,jackscrew 118 is turned in the opposite direction to develop thenecessary tension on chains 64 once more. Pillow blocks 53 supportingdrive shaft 52 are constructed similarly to that of pillow blocks 120,except that they are usually held stationary on supports 54. Jackscrews124 bearing against pillow blocks 53 merely ensure against lateralinward movement of fixedly mounted pillow blocks 53 as chains 64 turn.

As an auxiliary feature of the apparatus, means 126 are provided forclamping sheet S in place when it is a stationary position betweenintermittent movements. These means help to minimize sagging of thesheet during forming trimming, i.e. at times other than during itsadvancement. These means 126 comprise dual, oppositely aligned, grippingfingers 128 reciprocatably mounted by means of conventional fluidactuated pistons in housings 130, and are identical to the means forgripping sheet S during its advancement, except that they are fixedlymounted by means of brackets 132 to stringer 18 (FIG. 3) at the rearside of the equipment.

ln operation, DC motor 41 of drive means 38 is continuously energized.At the start of a cycle, carriage 22, as a result of the action ofdeadweight 92 pulling it under the influence of gravity along supportmembers, is at the rearmost position of the apparatus. On receiving asuitable control signal, fingers 34 reciprocate downwardly to pinchsheet S against support 32 of carriage 22, and cause clutch 41 toengage, thereby transmitting power from motor 40 through gearbox 44 toindexing mechanism 42. indexing mechanism 42, converts the 360 inputshaft rotation from gearbox 44 and transmits only an angular portionthereof, e.g. 120 to indexer drive gear 48. This l20 rotation is in turntransmitted through drive gear 50, drive shaft 52 and drive sprockets 58to chains 64. Sprockets 58 and drive gear 50 are sized for 360 rotationfor whatever the amount of angular rotation of the output shaft of theindexing mechanism. Likewise, the distance from one point on a pusherassembly to a corresponding point on one of the other pusher assemblieson a given side of the apparatus is equal to the length of one pitchline circumference of a sprocket 58 times 1r, or in other words is equalto two times the pitch radius of the sprocket times rr. As a result ofthe number and spacing of the pusher assemblies, one will always be atthe rear end of the apparatus after completion of the forward movementportion of a cycle in a position ready to engage drive piston 70 to movecarriage 22 forward for the next cycle under the influence of rotatingchains 64 of drive means 38. Previous to the start of a cycle each drivepiston 70 is caused to reciprocate outwardly through an outer ear 73 ofa yoke 28 by means of a suitable control signal, in order to permitengagement therewith in the cutout portion of enlarged section 82 ofplunger 78 (FIG. 5) of a pusher assembly. With the plunger and drivepiston 70 thus engaged, the motion of the drive means is transmitted tothe carriage and-controlled by the changing rate of angular rotation ofthe output shaft 46 of indexing mechanism 42, in order to advancesheet Sas smoothly as possible in as short a time as possible. Output shaft 46initially builds up to a relatively high angularvelocity in order tocorrespondingly move carriage 22 at a relatively high rate of speed forthe initial portion of the forward stroke. After carriage 22 andtherefore sheet S have advanced a percentage of the desired totaladvancement, e.g. about 50 percent, or just beyond end 116 of cam 112(FIG. 1) in moving from left to right, output shaft 46 of indexingmechanism 42 commences to slow down or decelerate. At this point,itbecomes necessary to transmit this deceleration to carriage 22, whichis being pushed along by plunger 78 and piston 70. This is accomplishedby means of stepped portion 107 of latch 106 bearing against rear face108 of a block 76 of the particular set of pusher assemblies then movingcarriage 22 forward. During the initial acceleration portion of theforward stroke of the equipment, latch 106 attached to yoke 28 ofcarriage 22 rides in track 114 of cam 112 as carriage 22 advances. As isapparent, (FIG. 5) drive piston 70 is being pushed forward by plunger 78in block 76, which in turn is mounted on chain 64, and is unconfined onits forward side. The decelerated motion resulting from the operation ofindexing mechanism 42 otherwise would not be transmitted to carriage 22except for the contact between latch 106 and block 76. Carriage 22 thuscontinues to advance until the output shaft of indexing mechanism 42ceases to rotate, whereupon the brake portion of clutch 41 isautomatically engaged by means of a suitable control signal, followed bydisengagement of the clutch portion of assembly 41, therebydiscontinuing the transmission of power to indexing mechanism 42 fromdrive motor 40. The internal parts of indexing mechanism 42 areconventionally designed to terminate rotation of its output'shaft 46substantially at the end of the desired extent of forward advancement ofcarriage 22. The forward movement of carriage 22, however, is positivelyterminated as a result of the impingement of the rear surface 134 oflatch 106 against forward stops which, as previously mentioned, arefixedly mounted on elongated cam 86. Thus, the extent of the forwardmovement of the carriage 22 and therefore of sheet S clamped thereon ispositively delimited by the position of the fixed forward stop 100.However, indexing mechanism 42, as well as the portions of drive means38 between output shaft 46 of indexing mechanism 42 and drive pistons 70have built in angular tolerances which otherwise will affect theaccuracy of the extent of advance of a sheet section. Thus, if theforward stroke of carriage 22 were not positively terminated by contactwith stop 100, carriage 22 would drift a small but highly significantamount equivalent to the extent of this tolerance, for example on theorder of 0.010 to 0.080 inch. As an important part of this invention,resiliently biased plunger 78 absorbs this movement, while permittingthe stroke to be delimited by the position of stationary forward stop100. 'In other words, this tolerance is never transmitted to thecarriage and sheet movement. Thus, during forward movement of carriage22, compression spring 83 is designed such that plunger 78, whileengaging drive piston 70, is kept in its foremost, maximum extendedposition. When surface 134 of latch 106 strikes stop 100 to terminatethe forward advance of carriage 22, plunger 78 moves to the rear inopposition to the forward urging of spring 83, an amount equivalent tothe extent of the tolerances inherently present in the drive system.Thus, the extent of movement of plunger 78 must at least be equal to andpreferably slightly in excess of the maximum amount of tolerances in thedrive system in order for the equipment to work properly, otherwiseplunger 78 will not be sufficiently compressed at the termination of theforward stroke and mechanical failure of one or more of the parts willoccur.

On termination of the forward stroke of carriage 22, stationary clampingmeans 126 may then be activated to hold sheet S in place during theforming and trimming operations of the upstream equipment. Drive piston70 is caused to reciprocate inwardly towards the axis of the apparatus,thereby disengaging it from contact with plunger 78 and permittingcarriage 22 to reciprocate freely to the rear position of the apparatuson support members under the influence of the gravity pull exertedthereon by deadweight 92. When carriage 22 strikes nose portion 136 onthe end of piston 138 adjustable stop 98, its rearward motion isterminated. During rearward movement of carriage 22, latch 106, which ispivotally mounted to yoke 28, of the carriage assembly rides up inclinedtrack 114 of cam 116, and at the termination of the rearward stroke ofthe carriage is positioned just behind the rear side 108 of the block 76of the pusher assembly which will carry out the next cycle, therebyleaving it in position to decelerate carriage 22 after commencement ofthe next forward stroke of the equipment in the manner previouslydescribed. The rearmost position of the carriage assembly as a result ofthe location of adjustable stop 98 will be such that drive pistons 70are just forward of plungers 78 of the next pusher assemblies to permitengagement of these parts when pistons 70 are caused to reciprocateoutwardly and chains 64 begin to turn. After completion of the necessaryupstream forming and trimming operations a suitable control signal istransmitted to the clutch 41 of drive means 38 to thus transmit rotationto gearbox 44 from drive motor 40 in order to commence another cycle ofthe apparatus. Just prior thereto, stationary clamping means 126 must,of course, be disengaged from the sheet.

Though many of the components of the sheet advance apparatus of theinvention have been depicted in the drawings and described as existingin duplicate on both sides of the axis of the apparatus, for example,the pusher assemblies, drive chains and sprockets, elongated cams, fixedstops etc. these components may be used singly if suitably designed interms of mechanical strength to withstand the forces generated duringmovement of the various parts.

Although the invention has been described in some detail, it is obviousthat many variations and modifications may be made thereof withoutdeparting from its spirit and scope.

What is claimed is:

1. Apparatus for intermittently advancing successive equivalent lengthportions of a thermoplastic sheet which comprises:

a. a frame;

b. a pair of horizontally disposed elongated support members on saidframe;

c. a carriage mounted for reciprocative movement on said supportmembers;

d. means on the carriage for gripping the sheet;

e. drive means for intermittently moving the carriage forward, saiddrive means including a rotary indexing mechanism for controlling thevelocity of the carriage during its forward movement so as to advancethe sheet smoothly when engaged by the gripping means;

f. means interconnecting the carriage to the drive means;

g. means for reversing the forward movement of the carriage; and

h. stops for delimiting the reciprocative movement of the carriage.

2. The apparatus of claim 1 wherein the drive means includes an endlesschain mounted on sprockets and the means interconnecting the carriage tothe drive means includes (a) a plurality of pusher assemblies fastenedto the endless chain at spaced, equidistant intervals about theperiphery of the chain and (b) a reciprocally mounted drive rod on thecarriage adapted to consecutively engage each of the pusher assembliesat the start of the forward movement of the carriage.

3. The apparatus of claim 2 wherein each pusher assembly comprises ablock fastened to said chain, said block having a plunger mountedtherein adapted to engage the drive rod on the carriage to move thecarriage forward, said plunger being resiliently biased in the directionof forward movement of the carria e.

4. 'fi-ie apparatus of claim 2 including means to decelerate the forwardmovement of the carriage prior to engagement of the carriage with one ofsaid stops, said decelerating means including a pivotally mounted latchon the carriage adapted to engage the rear side of one of the blocksduring forward movement of the carriage.

5. The apparatus of claim 3 wherein the pusher assembly has a camfollower mounted on each block and including an elongated cam on theframe having a track formed therein adapted to accept the follower fortravel therein as the chain turns.

6. The apparatus of claim 4 including means for moving the latch to therear side of the block of each pusher assembly prior to the start of theforward movement of the carriage.

7. The apparatus of claim 6 wherein the means for moving the latch tothe rear of each block includes a cam follower on the latch and a fixedcam having an upwardly inclined track formed therein adapted to engagethe follower on the latch during the reverse movement of the carriage,so as to elevate the pivotally mounted latch above the block of thepusher assembly which is to engage the drive rod for the next forwardmovement of the carriage.

8. The apparatus of claim 1 wherein the means for reversing the forwardmovement of the carriage comprises a flexible member associated at oneend with the carriage and at its other end with a weight, and a rotarymember on the frame peripherally engageable with said flexible memberintermediate said ends, whereby the weight pulls the carriage in theopposite direction from the forward movement after disengagement of thesheet from the gripping means.

9. The apparatus of claim 1 wherein said stops comprise an adjustablestop and a fixed stop, each stop being mounted on the frame, said stopsbeing spaced from each other on the frame a distance equivalent to theextent to which the sheet is moved forward during one intermittentmovement by the drive means.

10. The apparatus of claim 1 wherein the means for gripping the sheetcomprises oppositely aligned reciprocatably mounted fingers.

11. The apparatus of claim 1 including means for clamping the sheetalong the outer margins thereof when in a stationary position betweenintermittent movements.

12. In apparatus for forming multiple hollow articles such as containersand the like from a sheet of thermoplastic material including means forforcing portions of the sheet into mold cavities to form the containers,means for gripping the sheet while forming the containers, means forremoving the containers from the sheet after formation and meansdownstream of the removing means for intermittently advancing the sheetthrough the forming removing means, the improvement wherein the meansfor advancing the sheet comprises:

a. a frame;

b. a pair of horizontally disposed elongated support members on saidframe;

c. a carriage mounted for reciprocative movement on said supportmembers;

d. means on the carriage for gripping the sheet;

e. drive means for intermittently moving the carriage forward includingan indexing mechanism for controlling the velocity of the carriageduring its forward movement so as to advance the sheet smoothly whenengaged by the gripping means;

f. means interconnecting the carriage to the drive means;

g. means for reversing the forward movement of the carriage; and

h. stops for delimiting the reciprocative movement of the carriage.

1. Apparatus for intermittently advancing successive equivalent lengthportions of a thermoplastic sheet which comprises: a. a frame; b. a pairof horizontally disposed elongated support members on said frame; c. acarriage mounted for reciprocative movement on said support members; d.means on the carriage for gripping the sheet; e. drive means forintermittently moving the carriage forward, said drive means including arotary indexing mechanism for controlling the velocity of the carriageduring its forward movement so as to advance the sheet smoothly whenengaged by the gripping means; f. means interconnecting the carriage tothe drive means; g. means for reversing the forward movement of thecarriage; and h. stops for delimiting the reciprocative movement of thecarriage.
 2. The apparatus of claim 1 wherein the drive means includesan endless chain mounted on sprockets and the means interconnecting thecarriage to the drive means includes (a) a plurality of pusherassemblies fastened to the endless chain at spaced, equidistantintervals about the periphery of the chain and (b) a reciprocallymounted drive rod on the carriage adapted to consecutively engage eachof the pusher assemblies at the start of the forward movement of thecarriage.
 3. The apparatus of claim 2 wherein each pusher assemblycomprises a block fastened to said chain, said block having a plungermounted therein adapted to engage the drive rod on the carriage to movethe carriage forward, said plunger being resiliently biased in thedirection of forward movement of the carriage.
 4. The apparatus of claim2 including means to decelerate the forward movement of the carriageprior to engagement of the carriage with one of said stops, saiddecelerating means including a pivotally mounted latch on the carriageadapted to engage the rear side of one of the blocks during forwardmovement of the carriage.
 5. The apparatus of claim 3 wherein the pusherassembly has a cam follower mounted on each block and including anelongated cam on the frame having a track formed therein adapted toaccept the follower for travel therein as the chain turns.
 6. Theapparatus of claim 4 including means for moving the latch to the rearside of the block of each pusher assembly prior to the start of theforward movement of the carriage.
 7. The apparatus of claim 6 whereinthe means for moving the latch to the rear of each block includes a camfollower on the latch and a fixed cam having an upwardly inclined trackformed therein adapted to engage the follower on the latch during thereverse movement of the carriage, so as to elevate the pivotally mountedlatch above the block of the pusher assembly which is to engage thedrive rod for the next forward movement of the carriage.
 8. Theapparatus of claim 1 wherein the means for reversing the forwardmovement of the carriage comprises a flexible member associated at oneend with the carriage and at its other end with a weight, and a rotarymember on the frame peripherally engageable with said flexible memberintermediate said ends, whereby the weight pulls the carriage in theopposite direction from the forward movemEnt after disengagement of thesheet from the gripping means.
 9. The apparatus of claim 1 wherein saidstops comprise an adjustable stop and a fixed stop, each stop beingmounted on the frame, said stops being spaced from each other on theframe a distance equivalent to the extent to which the sheet is movedforward during one intermittent movement by the drive means.
 10. Theapparatus of claim 1 wherein the means for gripping the sheet comprisesoppositely aligned reciprocatably mounted fingers.
 11. The apparatus ofclaim 1 including means for clamping the sheet along the outer marginsthereof when in a stationary position between intermittent movements.12. In apparatus for forming multiple hollow articles such as containersand the like from a sheet of thermoplastic material including means forforcing portions of the sheet into mold cavities to form the containers,means for gripping the sheet while forming the containers, means forremoving the containers from the sheet after formation and meansdownstream of the removing means for intermittently advancing the sheetthrough the forming removing means, the improvement wherein the meansfor advancing the sheet comprises: a. a frame; b. a pair of horizontallydisposed elongated support members on said frame; c. a carriage mountedfor reciprocative movement on said support members; d. means on thecarriage for gripping the sheet; e. drive means for intermittentlymoving the carriage forward including an indexing mechanism forcontrolling the velocity of the carriage during its forward movement soas to advance the sheet smoothly when engaged by the gripping means; f.means interconnecting the carriage to the drive means; g. means forreversing the forward movement of the carriage; and h. stops fordelimiting the reciprocative movement of the carriage.